1. Field of the Invention
The subject invention relates to a method and apparatus for correcting nonlinearities in an analog signal. In particular, the invention is a method and apparatus for correcting nonlinear signals which uses digital techniques to adjust offset and gain while maintaining an entirely analog signal path.
2. Description of the Related Art
In many analog sensors (such as inductive position sensors, for example) the output is nonlinear over the operable range thereof. Linearization is often accomplished by reducing the range to one over which the sensor is substantially linear. However this reduced range limits the application of the sensor. Also, it is known to provide analog correcting circuits, such as log amps, to process the sensor output into a linear signal. However, this approach reduces the stability and increases the calibration difficulty of the circuit due to the introduction of additional analog components into the measuring circuit.
Certain modern manufacturing processes, such as positioning a photomask on a semiconductor during chip manufacturing, require that position measurement signals have linearities which are within one percent over a wide operating range. This has conventionally been accomplished by converting the analog measurement signal to a digital form and then processing it digitally before converting it back to an analog output. This method can be undesirable in that the resolution of the system is limited to that of the A/D and D/A converters. Also, a significant phase delay is introduced to the system due to processing time.